Question 100511
You have to use the distributive property for every term on the whole trinomial. It's messy, but you have to do it.
For example: {{{(x + y + z)^2}}}
{{{(x + y + z)^2 = x(x + y + z) + y(x + y + z) + z(x + y + z)}}}
In reality, this is what you are doing when you square a binomial. This works for any polynomial.